Several types of devices of selection and presentation of the weft yearns are already known.
According to one of these prior art devices a set of fingers, through whose eyelets the several weft yarns run, are hinged onto a corresponding set of actuation levers. The actuation levers are urged by a respective return spring against a stroke limit and are angularly moved by a corresponding set of selectors hinged to them. The selectors are urged by a respective return spring against a corresponding set of feeler needles of the weft yarns selection mechanism. The selectors can be shifted by a transverse oscillating beam supported by a cam-driven "L"-shaped lever which is urged against said cam by a return spring and cooperates with suitable appendices provided on all of said selectors. A further transverse beam is provided at the end of another--also cam-driven and spring returned--lever in order to simultaneously lift all of the selectors at each selection cycle.
In the presence of a selection hole in the perforated-tape or hole-closing-electromagnet mechanical program, the relevant feeler needle penetrates said hole, consequently moving downwards. Due to the effect of its return spring, the respective selector moves downwards and comes thus to a position in which it interferes with the movement of said oscillating beam. Such an interference will cause an oscillation of the same selector, and consequently of the respective actuation lever to take place, consequently causing an angular shift of the relevant arrow which will present its own, so selected, weft yarn, to the weft inserter organ.
Unfortunately, such a structure suffers from a plurality of mechanical drawbacks which are substantially due to the weft yarns selection mechanism The weft yarn selection mechanism with its feeler needles shows a poor precision at high speeds, and is extremely sensitive to dust, to moisture and to all changes in atmospheric conditions, which may cause the blocking thereof. On the other hand, said selection mechanism, with its moving parts, is subject to considerable wear and a consequent short useful life.